Electric steering wheel position adjustment apparatuses having various kinds of construction are known, and some are already being used as the steering apparatuses of automobiles. FIG. 19 illustrates a first example of conventional construction that was disclosed in JP 2010-116042 (A). The steering shaft 2 to which the steering wheel 1 is fastened has a cylindrical outer shaft, and a circular rod shaped inner shaft 4 that is inserted inside the outer shaft 3 so as to be able to move back-and-forth in the axial direction, and so as to be able to transmit torque. More specifically, there is a spline fit between the middle section to the front-end section of the inner circumferential surface of the outer shaft 3 and the outer circumferential surface of the rear-end section of the inner shaft 4. The steering wheel 1 is fastened to the rear-end section of the outer shaft 3.
The steering shaft 2 is inserted inside a cylindrical shaped steering column 5, and is supported so as to be able to freely rotate. The steering column 5 has a cylindrical outer column 6 that is supported by the vehicle body, and a cylindrical inner column 7 that is inserted inside the outer column 6 so as to be able to move back-and-forth in the axial direction. The portion near the rear end of the middle section of the outer shaft 3 is supported on the radially inside of the rear-end section of the inner column 7 so as to be prevented from displacing in the axial direction, and so as to be able to rotate freely. Moreover, the portion near the front end of the middle section of the inner shaft 4 is supported on the radially inside of the front-end section of the outer column 6 so as to be prevented from displacement in the axial direction, and so as to be able to rotate freely. With this construction, the steering shaft 2 is supported on the inside of the steering column 5 so as to be able to rotate freely, and the outer shaft 3 and inner column 7 are capable of relative movement in the forward-backward direction with respect to the inner shaft 4 and outer column 6.
The apparatus of the first example of conventional construction, as an electric actuator in order to be able to adjust the forward-backward position of the steering wheel 1, has: a gear housing 8 that is fastened to the bottom surface of the outer column 6; a feed nut 9 that is supported on the inside of the gear housing 8 so as to be prevented from displacement in the axial direction, and so as to be able to only rotate; a push-pull arm 10 that is fastened to a portion of the rear-end section of the inner column 7 that protrudes further toward the rear than the outer column 6; a push-pull rod 11 having a male screw section 12 provided on the front half thereof that screws into the feed nut 9, and the rear-end section thereof being linked with the push-pull arm 10; and an electric motor (omitted in the figure) that is connected to the feed nut 9 by way of a worm reducer 13, and that rotates and drives the feed nut 9.
When adjusting the forward-backward position of the steering wheel 1, the feed nut 9 is rotated, which causes the push-pull rod 11 to move in the axial direction. Due to this displacement, the inner column 7, by way of the push-pull arm 10, moves in the same direction as the push-pull rod 11, and by causing the outer shaft 3 that is supported on the inside of the inner column 7 to move in the forward-backward direction together with the inner column, the forward-backward position of the steering wheel 1 is adjusted.
In the electric steering wheel position adjustment apparatus of this first example of conventional construction, there is a possibility that the driver that operates the steering wheel 1 will experience an unpleasant or uncomfortable feeling due to a small space that exist in the area of fit between the rear-end section of the outer column 6 and the front-end section of the inner column 7. In other words, in the electric steering wheel position adjustment apparatus, differing from a manual apparatus, even in the state in which the adjusted position of the steering wheel 1 is maintained, the diameter of the rear-end section of the outer column 6 is not reduced, and a small space remains in the area of fit. Due to this small space, there is a possibility that the inner column 7 that supports the outer shaft 3 to which the steering wheel 1 is fastened will be loose with respect to the outer column 6 that is supported by the vehicle body. Due to this loose fit, the feeling of support rigidity of the steering wheel 1 will decrease, and there is a possibility that the driver that operates the steering wheel 1 will experience an unpleasant feeling. Moreover, this looseness causes the resonant frequency of the members of the electric steering wheel position adjustment apparatus that constitutes the steering column apparatus that includes the steering shaft 2 and steering column 5 to decrease, and when there is small vibration of the vehicle body when traveling over a bad road or the like, there is a possibility that unpleasant noise or vibration will occur in this steering column apparatus.
FIG. 20 and FIG. 21 illustrate a second example of conventional construction that is disclosed in JP 2006-297989 (A). In this second example of conventional construction as well, as in the first example of conventional construction, the steering shaft 2a is supported on the inside of the steering column 5a so as to be able to rotate freely, and the outer shaft 3a and inner column 7a are able move in the forward-backward direction relative to the inner shaft 4a and outer column 6a. 
In this second example of conventional construction, by using a linear motion ultrasonic motor 15 that is supported by the bottom-end section of an installation bracket 14 as an actuator in order to be able to adjust the forward-backward position of the steering wheel 1, it is possible for the inner column 7a to move in the axial direction with respect to the outer column 6a. More specifically, a moving piece 16 of the linear motion ultrasonic motor 15 and inner column 7a are linked by a transmission member 17, and by transmitting the movement of the moving piece 16 to the inner column 7a, it is possible to move the inner column 7a in the forward-backward direction. The base-end section of the transmission member 17 is fastened by screws to the inner column 7a, and the tip-end section of the transmission member 17 is linked to the moving piece 16 by way of a spherical joint 18. The spherical joint 18 has: an engaging concave section 19 that is formed in the moving piece 16; a spacer 20 that fits with and is supported by the engaging concave section 19, and that has an inner circumferential surface that is a spherical concave surface; and a spherical surface engaging section 21 that engages with the inner circumferential surface of the spacer 20.
When adjusting the forward-backward position of the steering wheel 1, the linear motion ultrasonic motor 15 causes the moving piece 16 to move in the axial direction of the steering column 5a. This displacement, by way of the transmission member 17, causes the inner column 7a to move in the same direction as the moving piece 16, which causes the outer shaft 3a that is supported on the inside of the inner column 7a to move in the forward-backward direction together with the inner column 7a. As a result, as illustrated by the two-dot chain line in FIG. 20, it becomes possible to adjust the forward-backward position of the steering wheel 1.
In the case of the construction of this second example of conventional technology, there is a problem in that due to the construction of the engagement area between the moving piece 16 and the transmission member 17, the manufacturing cost for maintaining smooth operation increases. In other words, in order to smoothly perform adjustment of the forward-backward position of the steering wheel 1 without any looseness, it is necessary to properly regulate the fitting strength at the engagement area between the spherical engaging section 21 of the transmission member 17 and the spacer 20. When the fitting strength is to low, a positive gap occurs in this engagement area, and looseness occurs between the spherical engaging section 21 and the spacer 20, which easily causes rattling of the steering wheel 1 in the forward-backward direction. On the other hand, when the fitting strength is too high, pivotal displacement of the spacer 20 with respect to the spherical engaging section 21 cannot be performed smoothly.
In the construction of this second example of conventional technology, the amount of movement in the forward-backward direction of the moving piece 16 is large, and unless there is a good degree of parallel accuracy between the movement direction of this moving piece 16 and the movement direction of the inner column 7a when performing forward-backward position adjustment of the steering wheel 1, as the forward-backward position of the steering wheel 1 is adjusted, the transmission member 17 will move in the axial direction of the transmission member relative to the moving piece 16. This relative displacement causes rubbing in the axial direction of the transmission member 17 between the outer circumferential surface of the spacer 20 and the inner circumferential surface of the engaging concave section 19. In this case, when the fitting strength is too high, and pivotal displacement of the spacer 20 with respect to the spherical engaging section 21 is not performed smoothly, there will be strong rubbing between the outer circumferential surface of the spacer 20 and the inner circumferential surface of the engaging concave section 19, and there is a possibility that noise or vibration will occur, causing the passengers in the automobile to experience an uncomfortable feeling. Particularly, in this state, the surface that allows relative displacement in the axial direction of the transmission member 17 between the transmission member 17 and the moving piece 16 is limited to only one location between the outer circumferential surface of the spacer 20 and the inner circumferential surface of the engaging concave section 19, so the rubbing length easily becomes long, which makes it even easier for noise and vibration to occur.
Performing high precision processing of the inner circumferential surface of the spacer 20, which is a spherical concave surface, and the outer circumferential surface of the spherical engaging section 21, which is a spherical convex section, in order to prevent the occurrence of noise and vibration is connected to higher costs. Moreover, when manufacturing the spherical engaging section 21 with high precision, it is not possible to avoid the outer diameter of the transmission member 17 becoming small on the base-end section of the spherical engaging section 21. It is easy for large stresses to occur in the neck section of this transmission member 17 during adjustment of the forward-backward position of the steering wheel 1, and so such construction as this is not advantageous from the aspect of maintaining sufficient durability when used over a long period of time.
As construction for preventing the occurrence of noise and vibration in the portion of the steering column apparatus, JP 5,076,908 (B2), for example, discloses a mechanism as illustrated in FIG. 22 in which support holes 22 are provided in part in the axial direction of the outer column 6b, and adjustment screws 24 that are screwed into female threads 23 that are formed in the support holes 22 press synthetic resin pads 26 that come in contact with the outer circumferential surface of the inner column 7b by way of disc springs 25, which prevents looseness of the portion that constitutes the steering column apparatus. However, in this mechanism, when the force by which the pads 26 press against the outer circumferential surface of the inner column 7b is made large enough to be able to prevent looseness, the drive load on the electric motor increases, and there is a problem in that the operation noise becomes large.